1. Field of the Invention
The present invention relates to a distance measuring device for a camera.
2. Description of Related Art
The present applicant has proposed a distance measuring device having a row of a plurality of SPDs (silicon photodiodes), as disclosed by Japanese Patent Application No. 8-248116 (which is incorporated herein by reference). According to this device, in order to avoid the influence of scattered light, infrared light from a light emitting element reflected by an object is received by a row of SPDs and a distance to the object is calculated from a ratio of output currents of a coupled double-cell having the largest amount of received light.
However, applicant's previous distance measuring device has a problem in that there is no assurance that all of the light from the light emitting element is reflected by the object to be photographed. For example, when the object is a person and light from the light emitting element is incident on the shoulder of the person, a portion of light may pass over and to the rear side of the person's shoulder, thereby altering the optical gravitational center of the reflected light and causing the distance to be erroneously measured. Hereinafter, such a phenomenon will be referred to as "beam deficiency".
As a distance measuring device in which it is difficult to solve the "beam deficiency" problem, there has conventionally been known a distance measuring device for a camera of an active type using a plurality of light emitting elements (hereinafter, referred to as "multiple AF (Automatic Focusing)"). The device is pointed toward an object, measuring light such as infrared light or the like is emitted, reflected light from the object is received by photocells and a distance to the object is determined based on positions at which images of the respective light emitting elements are formed on the photocells and the intensity of the received light.
However, when the multiple AF is formed by simply increasing the number of light emitting elements, as disclosed in Japanese Patent Application No. 8-248116 (incorporated herein by reference), the sequence becomes excessively complicated and the shutter release time lag is greatly prolonged, which reduces photo opportunity.